1. Field of the Invention
The present invention generally relates to liners for electrical contacts within integrated circuit chip devices and more particularly to a nitride enhanced titanium liner for a refractory metal contact formed using a chemical vapor deposition process.
2. Description of the Related Art
As the device densities of integrated circuits increase, there is a need to utilize metallurgies that can be conformally coated over the resulting steep topologies. It has been found that the family of metals commonly referred to as the xe2x80x9crefractory metals,xe2x80x9d (i.e., tungsten, titanium, molybdenum, nickel, etc.) can be conformally coated on substrates using low pressure chemical vapor deposition techniques (LPCVD). In these techniques, a refractory metal source gas (e.g., tungsten hexafluoride) undergoes a series of reduction reactions so as to deposit a layer of tungsten on the substrate.
One of the problems with utilizing a refractory metal such as tungsten is that it has a poor degree of adhesion to the underlying insulator (e.g., silicon oxide). One method of increasing the adhesion between the refractory metal and the underlying layers is to incorporate an intermediate material having a high degree of adhesion to both the refractory metal and the underlying materials. As disclosed in U.S. Pat. No. 5,769,475 to Cronin et al. (hereinafter xe2x80x9cCroninxe2x80x9d), incorporated fully herein by reference, an intermediate layer of titanium nitride, hafnium, zirconium, niobium, vanadium, chromium or nickel will provide a high degree of adhesion between tungsten and underlying layers.
In most applications, conductive structures such as gate electrodes and interconnecting stacks should have sidewalls that are as nearly vertical as possible. To the extent that these sidewalls are not vertical, extra chip surface area is unnecessarily consumed and the electrical properties of the conductive structure are degraded. Accordingly, the intermediate layer incorporated between the refractory metal and the underlying layers should have an etch rate that approximates the etch rate of refractory metal in an anisotropic (i.e., directional) etch, such as a halogen-based reactive ion etch (RIE). It has been discovered that titanium nitride has an etch rate that is substantially equal to tungsten in a halogen-based RIE, which permits an isotropic profile to be easily achieved.
As mentioned above, to form a conformal coating of tungsten or molybdenum, chemical vapor deposition (CVD) techniques are preferred to sputtering or evaporation techniques. In CVD of tungsten, tungsten reduction is induced from a tungsten hexafluoride (WF6) source gas. As a consequence, tungsten crystals form and grow on the underlying layers. The ability of these crystals to form and grow (i.e., nucleate) on the underlying layers is essential to providing a uniform film. Cronin discloses that titanium nitride present good nucleation sites for CVD tungsten or molybdenum.
Cronin also discloses that titanium nitride provides good barrier properties when incorporated in a tungsten-titanium nitride stack. In the case where tungsten is used as an interconnect structure or as a wiring plane, titanium nitride provides sufficient resistance against electromigration. Moreover, titanium nitride prevents diffusion of species (e.g., silicon) from the underlying layers into the tungsten at processing temperatures of up to 1000xc2x0 C. Also, titanium nitride serves as a good barrier against fluorine penetration during CVD of tungsten. In addition, a tungsten-titanium nitride conductive stack provides an extremely low contact resistance.
It is, therefore, an object of the present invention to provide a process of forming a refractory metal liner that includes depositing a layer of refractory metal on a first conductive layer, where at least half of the depositing is carried out in the presence of an amount of passivating agent that is sufficient to impede subsequent reaction of at least a top half of the layer of refractory metal with the first conductive layer and is less than an amount of passivating agent necessary to form a stoichiometric refractory metal with the passivating agent. The process also includes annealing the refractory metal and the first conductive layer in a first element ambient, thereby forming a stoichiometric refractory metal with the first element in at least a portion of the top half of the layer of refractory metal.
The depositing step forms a barrier in a central portion of the layer of refractory metal. The barrier impedes impurities from diffusing through the layer of refractory metal during the annealing process. The impurities include silicon impurities. The process also includes forming a second conductive layer over the layer of refractory metal in a chemical vapor deposition process, wherein the barrier impedes impurities from diffusing through the layer of refractory metal during the chemical vapor deposition process. These impurities include fluorine impurities.
The refractory metal can be either tungsten, titanum, molybdenum or nickel. The passivating agent can be nitrogen and/or chlorine, and the first element can be hydrogen, nitrogen, and/or ammonia.
Another embodiment of the invention forms an electrical connection in an integrated circuit chip and includes depositing a liner on a first conductive layer. A portion of the depositing is carried out in the presence of a passivating material, wherein the passivating material combines with the liner to form a barrier. The barrier impedes impurities from diffusing from the first conductive layer through the liner. The process also includes annealing the liner and the first conductive layer in a first element ambient, forming a second conductive layer over the liner. The barrier impedes the impurities from diffusing from said second conductive layer through the liner during the forming of the second conductive layer.
Another embodiment of the invention is a refractory metal liner that has a barrier that includes a passivating agent. The barrier impedes a subsequent reaction of at least a top half of the refractory metal liner with an adjacent conductive layer, an amount of the passivating agent in the barrier being less than an amount necessary to form a stoichiometric combination of the refractory metal liner and the passivating agent.
The barrier impedes impurities from diffusing from the first conductive layer through the refractory metal. These impurities includes silicon impurities. There is also a second conductive layer positioned over the refractory metal. The barrier impedes impurities from diffusing from the second conductive layer through the refractory metal. These impurities include fluorine impurities. The refractory metal can be either tungsten, titanum, molybdenum or nickel and the passivating agent can be nitrogen and/or chlorine.
Another embodiment is an electrical connection in an integrated circuit chip. The electrical connection includes a first conductive layer and a liner on the first conductive layer. The liner includes a barrier that impedes impurities from diffusing from the first conductive layer through the line. The invention also includes a second conductive layer over the liner. The barrier impedes the impurities from diffusing from the second conductive layer through the liner.
The sub-stoichiometric barrier of the passivating agent helps keep the liner from bonding with impurities during the annealing process by bonding the central portion of liner with the passivating agent instead of with the impurities. By including the passivating agent in the central portion of the liner, there is less free liner material available to bond with the impurities during the annealing process. Thus, any such impurities which bond with the liner will be principally limited to the upper portion of the liner. For example, titanium is highly reactive and will absorb oxygen (e.g., an impurity) very quickly when annealed. The fixed passivating agent barrier limits the oxidation of the upper portion of the liner.
The fixed passivating agent barrier similarly limits the amount of liner material that is available to bond with impurities (e.g., silicon) diffusing from lower layers. Thus, the barrier layer prevents, for example, silicon agglomeration during the annealing process. By reducing the amount of silicon in the liner, the formation of fluorine compounds is reduced during the subsequent fluorine based chemical vapor deposition.